In sentences like these, that is used to indicate result, but a result is "a thing that is caused or produced by something else" which would imply that at some point, the thing was not the thing indicated by "that." That means at some point, the movie wasn't hilarious, that plants could be grown, and that people could buy the jewel, but that doesn't seem right, but if "that" doesn't indicate result in these sentences, I'm not sure how else to define it.

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I mean I guess it could be taken either way. You could use result clauses like that to imply a causality that happened over time, or you could also use them to imply an immediate causality — one where because of the condition, the result was always the case. I don't think anyone's ever sat down and rigorously defined which way to take it.